Large balloons have been widely used for advertisement and other purposes. FIG. 11 of the attached drawings shows an example of a conventional balloon having an airship-shape, designated by reference A. The balloon A has a number of tail fins B integrally formed with the balloon A whereby when the balloon A is inflated, air gets into the fins B and expands the fins B. The expanded or inflated fins B are kept in shape and position by the compressed air filled therein. Besides decoration, the fins B serve no purposes.
Thus, it is desired to provide a fin structure of a balloon which also serves to stabilize the balloon.